1. Field of the Invention
The present invention relates to a display device and, more specifically, to a power control apparatus of a display device that measures an output current to a display panel and adjusts a power supply voltage and a cathode voltage to maintain the output current within designated conditions, thus preventing damage to the display panel due to excessive current and deterioration.
2. Discussion of the Related Art
Recently, portable electronic devices, such as portable handsets, notebooks, personal computers and personal data assistants, have become widely used. A display device, such as a liquid crystal display (LCD) or an electroluminescence (EL) display, is typically used as the display device in these portable electronic devices due to their low power consumption. The organic EL display and the LCD, which uses an organic EL device as a light emitting source, arrange, drive and control a plurality of display pixels by turning them on or off to display a desired image. Generally, the display device drives the pixels by supplying a power supply voltage and a cathode voltage to the panel. Typically, a low voltage power supply of 2.8˜3.3V is used to drive the panel. A DC-DC converter raises the power supply voltage to +5V or reduces it to −6V and outputs that voltage to the display device.
FIG. 1 is a block diagram of a conventional display device.
A data driver 10 outputs a data signal to a pixel 51, a scan driver 20 outputs a selection signal to the pixel 51, a DC-DC converter 30 raises or reduces an input power supply voltage to output to the pixel 51, a control unit 40 controls each component, a panel 50 displays a certain image, and the pixel 51 displays a certain color on the panel 50.
As shown in FIG. 1, the panel 50 has a plurality of scan lines S1 . . . Sm and a plurality of data lines D1 . . . Dz, arranged in rows and columns and connected to the scan driver 20 and the data driver 10, respectively. A plurality of pixels 51 are arranged at their intersections. Further, each pixel 51 is connected to a first level of power supply voltage line 52 and a second level of power supply voltage line 53, which are connected to the DC-DC converter 30. Further, the DC-DC converter 30 is connected to the control unit 40, and the control unit 40 is also connected to the scan driver 20 and the data driver 10.
For the conventional display device with the above configuration, when the control unit 40 transmits a driving control signal to the DC-DC converter 30, the DC-DC converter 30 raises or reduces the provided power supply voltage (not shown) to apply, for example, +5V to the first level of power supply voltage line 52 and −6V to the second level of power supply voltage line 53.
Further, the control unit 40 applies the driving control signal to the scan driver 20 and the data driver 10. The scan driver 20 outputs the selection signal to the pixel 51 through the appropriate scan line S1 . . . Sm, and the data driver 10 outputs a light emitting data signal to the pixel 51 through the appropriate data line D1 . . . Dz.
Therefore, each pixel 51 is turned on by the selection signal, and a certain color is emitted according to the data signal and the driving signal by the power supply voltage VDD and the cathode voltage VSS, so that the panel 50 displays the desired image.
However, the display device generally supplies the power supply voltage and the cathode voltage meeting conditions for driving each pixel, and when the panel's temperature goes beyond a certain range, the driving current transmitted to the panel may likewise go beyond a certain range, which may result in application of excessive current. The excessive current may cause excessive brightness, which causes panel deterioration and increases the current of a switching device provided to each pixel. Also, increased current may result in degraded efficiency of the panel.